In a photolithography step of manufacturing a semiconductor, a semiconductor manufacturing apparatus such as a stepper (reduced projection lithographic exposure apparatus) is used for forming a photoresist pattern corresponding to an integrated circuit on a wafer. A pellicle is a tensioned transparent thin film placed on one end surface of a pellicle frame and used for preventing foreign matter from directly adhereing to a mask for forming a circuit pattern. Accordingly, even if foreign matter adheres to a pellicle in a photolithography step, an image of the foreign matter is not formed on a wafer coated with a photoresist. Owing to this, e.g., short circuit and wire breakage of a semiconductor integrated circuit caused by an image of foreign matter can be prevented, with the result that yield in a photolithography step can be improved.
Usually, a pellicle is fixed on a mask with an adhesive for a pellicle and can be detached from the mask. As the adhesive, an acrylic-, rubber-, polybutene-, polyurethane- and silicone-based adhesives are known (see the following Patent Literature 1). An adhesive layer is formed on the other end surface of a pellicle frame on one end surface of which a tensioned pellicle film is provided. When a pellicle film or a mask is contaminated, the pellicle film is once peeled from the mask and dirt is removed and then the pellicle film needs to be provided again. Furthermore, in order to prevent removal of a pellicle from a mask in a lithographic exposure step, the above adhesive is required to have a sufficient adhesive strength (load bearing) for a pellicle not to peel off even if a predetermined load is applied to the pellicle.
Recently, with development of highly integrated semiconductor apparatus, exposure light having a shorter wavelength is increasingly used in a photolithography step. In other words, in drawing an integrated circuit pattern on a wafer, developing a technique for drawing a micro circuit pattern with a narrower line width is required. To deal with this, as exposure light for a photolithography stepper, for example, KrF excimer laser (wavelength 248 nm) and ArF excimer laser (wavelength 193 nm) and further F2 excimer laser (wavelength 157 nm), all having shorter wavelengths than g-line (wavelength 436 nm) and i-line (wavelength 365 nm) conventionally used, are going to be used.
With a tendency toward shorter wavelength and higher energy of exposure light, a pellicle film or a mask becomes frequently contaminated by lithographic exposure, with the result that a frequency of replacing the pellicle film or the mask increases.